Environmentally-friendly vehicles include a fuel cell vehicles, electric vehicles, plug-in electric vehicles, and hybrid vehicles, and typically include a motor to generate driving force.
A hybrid vehicle, which is an example of the environmentally-friendly vehicle, uses an internal combustion engine together with the power of a battery. In other words, the hybrid vehicle efficiently combines and uses the power of the internal combustion engine and the power of a motor.
The hybrid vehicle may include an engine, a motor, an engine clutch to adjust power between the engine and the motor, a transmission, a differential gear apparatus, a battery, a starter-generator that starts the engine or generates electricity by output of the engine, and wheels.
Further, the hybrid vehicle may include a hybrid control unit (HCU) for controlling the overall operation of the hybrid vehicle, an engine control unit (ECU) for controlling the operation of the engine, a motor control unit (MCU) for controlling the operation of the motor, a transmission control unit (TCU) for controlling the operation of the transmission, and a battery control unit (BCU) for controlling and managing the battery.
The battery control unit may also be referred to as a battery management system (BMS). The starter-generator may also be referred to as an integrated starter and generator (ISG) or a hybrid starter and generator (HSG).
The hybrid vehicle can be driven in a driving mode, such as an electric vehicle (EV) mode, which is an electric vehicle mode using only power of the motor, a hybrid electric vehicle (HEV) mode, which uses rotational force of the engine as main power and uses rotational force of the motor as auxiliary power, and a regenerative braking (RB) mode for collecting braking and inertial energy during driving by braking or inertia of the vehicle through electricity generation of the motor to charge the battery.
In a hybrid vehicle to which an electric four wheel drive (E-4WD) system is applied, independent driving devices are applied to front and rear wheels, respectively. In this case, an internal combustion engine (ICE) may be used as the driving device of the front wheels, and a driving motor may be used as the driving device of the rear wheels. The driving devices may be driven independently or together according to a driving environmental condition.
In a typical E-4WD hybrid vehicle, the vehicle is typically driven in a 2 wheel drive (2WD) mode in which the vehicle is driven by using only any one of front and rear wheels as a driving wheel. When driving power is insufficient, the vehicle is switched to a 4WD mode in which the vehicle is driven by using the other wheel in an idle state as the driving wheel.
In the E-4WD hybrid vehicle, the drive mode is changed depending on a driving situation so as to improve fuel efficiency. For example, when a slip occurs due to sudden starting, slippery road, sandy soil, steep hill, muddy path, or the like, and therefore, high driving power is required, the vehicle is driven in the 4WD mode. In normal high-speed driving, the vehicle is driven in the 2WD mode.
When the vehicle is driven in the 4WD mode, it is advantageous in terms of posture control or steering ability of the vehicle, climbing performance, and escape of rough road. However, in the 4WD mode, fuel efficiency is deteriorated as compared with that in the 2WD mode. When the vehicle is driven in the 2WD mode, driving torque is small, and there is no excess in terms of steering stability. However, in the case of a rainy road, snowy road, or frozen road, the road surface friction coefficient of the road decreases, and hence the friction limit of tires also decreases. Therefore, it is difficult to control the posture of the vehicle.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.